scholarly journals Prediction of Turbulent Boundary Layer Induced Noise in the Cabin of a BWB Aircraft

2012 ◽  
Vol 19 (4) ◽  
pp. 693-705 ◽  
Author(s):  
Joana Rocha ◽  
Afzal Suleman ◽  
Fernando Lau
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Sound Pressure ◽  
Pressure Level ◽  
Interior Noise ◽  
Analytical Models ◽  
Frequency Range ◽  
Noise Levels ◽  
Cabin Noise ◽  
Cabin Interior

This paper discusses the development of analytical models for the prediction of aircraft cabin noise induced by the external turbulent boundary layer (TBL). While, in previous works, the contribution of an individual panel to the cabin interior noise was considered, here, the simultaneous contribution of multiple flow-excited panels is analyzed. Analytical predictions are presented for the interior sound pressure level (SPL) at different locations inside the cabin of a Blended Wing Body (BWB) aircraft, for the frequency range 0–1000 Hz. The results show that the number of vibrating panels significantly affects the interior noise levels. It is shown that the average SPL, over the cabin volume, increases with the number of vibrating panels. Additionally, the model is able to predict local SPL values, at specific locations in the cabin, which are also affected with by number of vibrating panels, and are different from the average values.

Prediction of Turbulent Flow-Induced Noise in Aircraft Cabins

2010 ◽  
Author(s):  
Joana da Rocha ◽  
Afzal Suleman ◽  
Fernando Lau
Keyword(s):  
Turbulent Flow ◽  
Analytical Model ◽  
Sound Pressure ◽  
Real Life ◽  
Interior Noise ◽  
Analytical Models ◽  
Aircraft Cabins ◽  
Wide Range ◽  
Flow Induced Noise ◽  
Cabin Interior

Flow-induced noise in aircraft cabins can be predicted through analytical models or numerical methods. However, the analytical methods existent nowadays were obtained for simple structures and cabins, in which, usually, a single panel is excited by the turbulent flow, and coupled with an acoustic enclosure. This paper discusses the development of analytical models for the prediction of aircraft cabin noise induced by the external turbulent boundary layer (TBL). The coupled structural-acoustic analytical model is developed using the contribution of both structural and acoustic natural modes. While, in previous works, only the contribution of an individual panel to the cabin interior noise was considered, here, the simultaneous contribution of multiple flow-excited panels is also analyzed. The analytical models were developed for rectangular and cylindrical cabins. The mathematical models were successfully validated through the good agreement with several independent experimental studies. Analytical predictions are presented for the interior sound pressure level (SPL) at different locations inside the cabins. It is shown that identical panels located at different positions have dissimilar contributions to the cabin interior noise, showing that the position of the vibrating panel is an important variable for the accurate prediction of cabin interior noise. Additionally, the results show that the number of vibrating panels significantly affects the interior noise levels. It is shown that the average SPL, over the cabin volume, increases with the number of vibrating panels. The space-averaged SPL is usually accepted to provide the necessary information for the noise prediction. However, in some real life applications, the local sound pressure may be desirable. To overcome this point, the model is also able to predict local SPL values, at specific locations in the cabin, which are also affected by number of vibrating panels, and often differ from the average SPL values. The developed analytical model can be used to study a wide range of different systems involving a cabin coupled with vibrating panels, excited by the TBL. The properties of the external flow, acoustic cabin, and panels, as well as the number of vibrating panels, can be easily changed to represent different systems. These abilities of the model make it a solid basis for future investigations involving the implementation of noise reduction techniques and multidisciplinary design optimization analyzes.

Flow-Induced Noise and Vibration in Aircraft Cylindrical Cabins: Closed-Form Analytical Model Validation

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Joana da Rocha ◽  
Afzal Suleman ◽  
Fernando Lau
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulent Flow ◽  
Closed Form ◽  
Experimental Studies ◽  
Interior Noise ◽  
Analytical Models ◽  
Simply Supported ◽  
Aircraft Cabin ◽  
Flow Induced Noise

The turbulent boundary layer is a major source of interior noise in transport vehicles, mainly in aircraft during cruise flight. Furthermore, as new and quieter jet engines are being developed, the turbulent flow-induced noise will become an even more important topic for investigation. However, in order to design and develop systems to reduce the cabin interior noise, the understanding of the physical system dynamics is fundamental. In this context, the main objective of the current research is to develop closed-form analytical models for the prediction of turbulent boundary-layer-induced noise in the interior of aircraft cylindrical cabins. The mathematical model represents the structural-acoustic coupled system, consisted by the aircraft cabin section coupled with the fuselage structure. The aircraft cabin section is modeled as a cylindrical acoustic enclosure, filled with air. The fuselage structure, excited by external random excitation or by turbulent flow, is represented through two different models: (1) as a whole circular cylindrical shell with simply supported end caps and (2) as a set of individual simply supported open circular cylindrical shells. This paper presents the results obtained from the developed analytical framework and its validation through the successful comparison with several experimental studies. Analytical predictions are obtained for the shell structural vibration and sound pressure levels, for the frequency range up to 10,000 Hz.

Research on Aerodynamic Noise of Base Styling Characteristics of Car Rearview Cover

2012 ◽  
Vol 490-495 ◽  
pp. 2987-2991
Author(s):  
Xin Chen ◽  
Jun Long Zhou
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Pressure Level ◽  
Interior Noise ◽  
Aerodynamic Noise ◽  
Theory Of Computation ◽  
Frequency Range ◽  
Digital Models ◽  
Compare Analysis

The 3-D digital models are established for two kinds of base styling of rearview cover. The compare analysis using Fluent model is based on the acoustic theory of computation. The results show that the average sound pressure level of up-raised rearview cover model is about 5 dB lower than that down-raised rearview cover model, and in all of the frequency range were apparently different. At the same time, the vortex of down-raised happened at the back location, which is more closer to the passenger’s ear, and affect the car interior noise. The results of analysis will conduct the design of rearview styling effectively.

scholarly journals Status of noise pollution in urban area of Dharan Sub- Metropolitan City and Inaruwa Municipality of Sunsari District, Nepal

2017 ◽  
Vol 7 (1) ◽  
pp. 35-40
Author(s):  
Ranij Shrestha ◽  
Alankar Kafle ◽  
Kul Prasad Limbu
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Pollution Assessment ◽  
Noise Pollution ◽  
Pressure Level ◽  
Noise Levels ◽  
Night Time ◽  
Level Measurement ◽  
Standard Value ◽  
Autumn And Winter

The environmental noise level measurement in Dharan and Inaruwa cities of eastern Nepal were conducted and compared with the ambient noise standards provided by Government of Nepal. The noise pollution assessment was performed in autumn and winter seasons by the indicator average day time sound pressure level (Ld, during 7.00 to 22.00 hrs) and average night time sound pressure level (Ln, during 22.00 to 7.00 hrs). The Ld and Ln values at the commercial, silence and residential zones of Dharan were 78 to 82 and 72 to 73, 65 to 73 and 60 to 70, 65 to 76 and 62 to 64 dB(A) in autumn and 78 to 79 and 72 to 76, 64 to 71 and 58 to 68, 63 to 74 and 60 to 62 dB(A) in winter, respectively whereas for Inaruwa, measurement were 75 to 77 and 73 to 75, 59 and 57, 67 and 60 dB(A) in autumn and 66 to 70 and 63 to 68, 55 and 53, 65 and 58 dB(A) in winter, respectively. The results showed that noise levels exceeded the standard value at most of the sites.

scholarly journals Reducing the harmful effects of noise on the human environment. Sound insulation of industrial skeleton enclosures in the 10–40 kHz frequency range

2020 ◽  
Vol 18 (2) ◽  
pp. 1451-1463
Author(s):  
Witold Mikulski
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Sheet Steel ◽  
Pressure Level ◽  
Sound Insulation ◽  
Frequency Range ◽  
Noise Sources ◽  
Human Environment ◽  
Absorbing Material ◽  
Acoustic Enclosures

Abstract Purpose The purpose of the research is to work out a method for determining the sound insulation of acoustic enclosures for industrial sources emitting noise in the frequency range of 10–40 kHz and apply the method to measure the sound insulation of acoustic enclosures build of different materials. Methods The method is developed by appropriate adaptation of techniques applicable currently for sound frequencies of up to 10 kHz. The sound insulation of example enclosures is determined with the use of this newly developed method. Results The research results indicate that enclosures (made of polycarbonate, plexiglass, sheet aluminium, sheet steel, plywood, and composite materials) enable reducing the sound pressure level in the environment for the frequency of 10 kHz by 19–25 dB with the reduction increasing to 40–48 dB for the frequency of 40 Hz. The sound insulation of acoustic enclosures with a sound-absorbing material inside reaches about 38 dB for the frequency of 10 kHz and about 63 dB for the frequency of 40 kHz. Conclusion Some pieces of equipment installed in the work environment are sources of noise emitted in the 10–40 kHz frequency range with the intensity which can be high enough to be harmful to humans. The most effective technical reduction of the associated risks are acoustic enclosures for such noise sources. The sound pressure level reduction obtained after provision of an enclosure depends on its design (shape, size, material, and thickness of walls) and the noise source frequency spectrum. Realistically available noise reduction values may exceed 60 dB.

scholarly journals Acoustic Simulation’s Verification of WFI ATHENA Filterwheel Assembly

2017 ◽  
Vol 42 (3) ◽  
pp. 483-489
Author(s):  
Adam Pilch ◽  
Tadeusz Kamisinski ◽  
Mirosław Rataj ◽  
Szymon Polak
Keyword(s):  
Main Part ◽  
Sound Pressure ◽  
Pressure Level ◽  
Noise Levels ◽  
Large Area ◽  
Fem Simulations ◽  
Absorbing Material ◽  
Reduce Risk ◽  
High Sound ◽  
Very High

Abstract Ariane 5 rocket produces very high sound pressure levels during launch, what can influence structures located in the fairing. To reduce risk of damage, launch in vacuum conditions is preferred for noise sensitive instruments. In Wide Filed Imager (WFI) project, the main part of the filterwheel assembly is an extremely thin (~240 nm) filter of large area (170×170 mm), very sensitive to noise and vibrations. The aim of this study was to verify numerical calculations results in anechoic measurements. The authors also checked the influence of WFI geometry and sound absorbing material position on sound pressure level (SPL) affecting the filter mounted inside the assembly. Finite element method (FEM) simulations were conducted in order to obtain noise levels in filter position during Ariane 5 rocket launch. The results will be used in designing of WFI filterwheel assembly and endurance of the filter during launch verification.

Electroacoustic Characteristics of Personal FM Systems

1982 ◽  
Vol 47 (4) ◽  
pp. 355-362 ◽  
Author(s):  
David B. Hawkins ◽  
Dianne J. Van Tasell
Keyword(s):  
Hearing Aids ◽  
Sound Pressure ◽  
Internal Noise ◽  
Pressure Level ◽  
Volume Control ◽  
Clinical Use ◽  
Noise Levels ◽  
Response Curves ◽  
Direct Input ◽  
System Configurations

Electroacoustic characteristics of various personal FM system configurations were obtained through the use of a Zwislocki ear simulator and KEMAR. Saturation Sound Pressure Level 90 and frequency response curves were obtained with different hearing aids in the microphone mode and then compared to the response obtained when the hearing aids were coupled to a FM receiver via neck loops and direct input. In addition, hearing aid orientation to and distance from the loop, clothing effects, internal noise levels, FM receiver volume control taper, and the effect of different FM receivers were investigated. The results indicated substantial microphone-teleloop response differences. Only minor differences were observed in the microphone-direct input comparison. Other variables were found that significantly affect the use of these personal FM systems. The results are discussed in terms of the implications for clinical use.

Wall Pressure Phase Velocity Measurements in a Turbulent Boundary Layer

2012 ◽  
Author(s):  
Teresa S. Miller ◽  
Mark J. Moeller
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Phase Velocity ◽  
Group Velocity ◽  
Noise Source ◽  
Wall Pressure ◽  
Interior Noise ◽  
Convection Velocity ◽  
Phase Velocities ◽  
Wall Pressure Fluctuation

The turbulent boundary layer that forms on the outer surfaces of vehicles can be a significant source of interior noise. In automobiles this is known as wind noise, and at high speeds it dominates the interior noise. For airplanes the turbulent boundary is also a dominant noise source. Because of its importance as a noise source, it is desirable to have a model of the turbulent wall pressure fluctuations for interior noise prediction. One important parameter in building the wall pressure fluctuation model is the convection velocity. In this paper, the phase velocity was determined from the streamwise pressure measurements. The phase velocity was calculated for three separation distances ranging from 0.25 to 1.30 boundary layer thicknesses. These measurements were made for a Mach number range of 0.1 < M < 0.6. The phase velocity was shown to vary with sensor spacing and frequency. The data collapsed well on outer variable normalization. The phase velocities were fit and the group velocity was calculated from the curve fit. The group velocity was consistent with the array measured convection velocities. The group velocity was also estimated by a band limited cross correlation technique that used the Hilbert transform to find the energy delay. This result was consistent with the group velocity inferred from the phase velocities and the array measured convection velocity. From this research, it is suggested that the group velocity found in this study should be used to estimate the convection velocity in wall pressure fluctuation models.

scholarly journals Noise-silencing technology for upright venting pipe jet noise

2018 ◽  
Vol 10 (8) ◽  
pp. 168781401879481 ◽  
Author(s):  
Enbin Liu ◽  
Shanbi Peng ◽  
Tiaowei Yang
Keyword(s):  
Natural Gas ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Low Frequency ◽  
Jet Noise ◽  
Pressure Level ◽  
Living Environment ◽  
Frequency Noise ◽  
Frequency Range ◽  
Expansion Chamber

When a natural gas transmission and distribution station performs a planned or emergency venting operation, the jet noise produced by the natural gas venting pipe can have an intensity as high as 110 dB, thereby severely affecting the production and living environment. Jet noise produced by venting pipes is a type of aerodynamic noise. This study investigates the mechanism that produces the jet noise and the radiative characteristics of jet noise using a computational fluid dynamics method that combines large eddy simulation with the Ffowcs Williams–Hawkings acoustic analogy theory. The analysis results show that the sound pressure level of jet noise is relatively high, with a maximum level of 115 dB in the low-frequency range (0–1000 Hz), and the sound pressure level is approximately the average level in the frequency range of 1000–4000 Hz. In addition, the maximum and average sound pressure levels of the noise at the same monitoring point both slightly decrease, and the frequency of the occurrence of a maximum sound pressure level decreases as the Mach number at the outlet of the venting pipe increases. An increase in the flow rate can result in a shift from low-frequency to high-frequency noise. Subsequently, this study includes a design of an expansion-chamber muffler that reduces the jet noise produced by venting pipes and an analysis of its effectiveness in reducing noise. The results show that the expansion-chamber muffler designed in this study can effectively reduce jet noise by 10–40 dB and, thus, achieve effective noise prevention and control.

Effects of Very Low Frequency Tones on Auditory Thresholds

1966 ◽  
Vol 9 (1) ◽  
pp. 150-160 ◽  
Author(s):  
J. Jerger ◽  
B. Alford ◽  
A. Coats ◽  
B. French
Keyword(s):  
Adverse Effects ◽  
Sound Pressure ◽  
Human Subjects ◽  
Low Frequency ◽  
Pressure Level ◽  
Variable Speed ◽  
Frequency Range ◽  
Auditory Thresholds ◽  
Very Low Frequency ◽  
Piston Cylinder

Nineteen human subjects were exposed to repeated three-minute tones in the sound pressure level range from 119 to 144 dB and the frequency range from 2–22 cps. The tones were produced in an acoustic test booth by a piston-cylinder arrangement, driven by a variable speed direct current motor. Eight subjects showed no adverse effects. Temporary threshold shifts (TTS) of 10 to 22 dB in the frequency range from 3 000 to 8 000 cps were observed in the remaining 11 subjects. In addition, the 7 and 12 cps signals produced considerable masking over the frequency range from 100 to 4 000 cps.

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